The characterization of atherosclerotic plaque will be investigated through the development and use of methods based on analysis of reflected ultrasonic signals taken with the sound beam perpendicular to the artery. These techniques will be useful in examination of non flow-obstructing plaque that causes symptoms, and in studies in progression/regression of plaque in humans. Signal measures to be used are, Doppler-shifted signals from radially-directed flow, vessel dimensions, plaque echo amplitude, plaque attenuation, and vessel wall structure based on cepstrum analysis. In addition, wall impedance and loss profiles will be obtained through use of exact inversion methods under development. Data will be obtained from phantoms for equipment calibration and as a check on accuracy of methods. Vessels from older cadavers containing visible plaque will be used to correlate ultrasound and pathology findings. Selected patients will be examined at Thomas Jefferson University Hospital Vascular Lab, and data correlated with x-ray and surgery specimens following protocols established and used for the B-mode assessment contact effort. Data will be digitized and stored on disk for initial off-line analysis at Drexel, on a system to be modified later to perform analysis in the clinic.